Polyurethanes, particularly polyurethane foams, have many uses in which fire retardancy is an important and highly desirable property. It is well-known to impart some degree of fire retardancy to polyurethane foams by incorporating into such foams a fire-retarding agent such as phosphorus. Most conveniently, the phosphorus is introduced as one component of the reaction medium, preferably the polyol reactant thereby simplifying the procedure and equipment necessary in order to produce the resulting polyurethane, but additionally providing a polyurethane wherein the phosphorus component is integrally bonded to the polymer and not merely physically incorporated.
It is already known to prepare phosphorus-containing polyether polyols by reaction of phosphoric acid with an alkylene oxide. For example, in U.S. Pat. No. 3,639,543, phosphoric acid and derivatives thereof were reacted with alkylene oxides such as ethylene oxide, propylene oxide, etc. Polyols prepared in this manner contain no added hydroxyl functionality and consequently are limited to the functionality of the initiator. Furthermore, these phosphorus-containing polyether polyols of the prior art have the inherent disadvantage of providing only terminal hydroxyl functionality, e.g., hydroxyl functionality only at the end of the polymer chain not pendant from the backbone. Attempts at providing other than terminal hydroxyl functionality, e.g., by reaction of glycidol with phosphoric acid, result in high molecular weight cross-linked residues due to reaction of the hydroxyl functionality.
Primary hydroxyl-containing polyether polyols made by reaction of tertiary butyl glycidyl ether alone or in combination with other alkylene oxides and suitable initiators followed by dealkylation are also known. In British Patent specification No. 1,267,259, tertiary butyl glycidyl ether is reacted with compounds or mixtures of compounds having one active hydrogen atom selected from alcohols, polyols, halogenated alcohols, water, thiols, mercapto-alkanols and phenols. Catalysts for the reaction include Lewis acids such as BF.sub.3, SnCl.sub.4, SbCl.sub.5, etc.
In U.S. Pat. No. 4,086,194, halogen- and hydroxyl-containing polymers are prepared by reaction of halides of alkyl and aryl phosphonic acids with glycidol. The compound was found to be a highly viscous material, probably due to reaction of hydroxyl functionality during the reaction as previously discussed. The product was added to a conventional polyol diluent prior to making of the polyurethane.
It is seen that conventional phosphorus-containing polyols have not been satisfactory. It is desirable to prepare a phosphorus-containing polyol containing pendant primary hydroxyl functionality thereby providing phosphorus-containing polyols of low hydroxyl number.
It is further desirable to prepare phosphorus-containing polyols that are not overly viscous liquids or intractable solids but instead are free-flowing liquids that may be used in the preparation of polyurethanes without the addition of a liquid diluent.
It is further desirable to provide phosphorus-containing polyols having high phosphorus and halogen content useful in preparing polyurethanes having increased flame retardancy.